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Old 09-09-2020, 05:00 AM   #1
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Calculating tongue weight requirements

I'm currently excitedly waiting for a International 27FB to be delivered, and see that the spec quotes "Hitch Weight (w/ LP & Batteries)" as 791lbs. Does anyone know how this number is calculated? Is it with nothing in the trailer (based on the unloaded weight of 5868lbs), or assuming a relatively pessimistic distribution with the full GVWR of 7600lbs? I think it's the former


I'm planning to install a Hensley Arrow hitch (weighing ~190lbs). Does this mean that my car needs to have 791+190=981lb tongue weight capability? I need to purchase a towing vehicle and know trucks are the best options, but would prefer an SUV. However, looking at these numbers, I suspect this makes that impossible...

Thanks!
Nick
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Old 09-09-2020, 05:29 AM   #2
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Welcome Aboard👍

"Assume" a tongue weight of at least 1000lb plus loaded for camping with the Hensley, AS is notoriously light with the numbers.

On the tow vehicle...pay attention to the front and rear axle weight ratings along with the load rating of the tires.(LT not passenger) stay under those and the payload will follow. Use the sticker specs as a guide.
The hitch receiver will have a sticker giving the TW with and without weight distribution.

POI....Install the HaHa yourself if possible, it's a good way to learn and understand. It's not all that hard. <READ THE MANUAL>

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Our TW...1200lb
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Old 09-09-2020, 05:47 AM   #3
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No, Nick, because the Hensley increases the distance from the receiver mouth to trailer axle dimension by 25", the actual Hensley weight increase at the receiver mouth increases by a surprisingly low ~70#.
I have calculated this with a 30' Classic dimension, verified with CAT scales as well as Sherline scale...and...had my calculations verified by an engineer relative.

And before the pot starts to boil, the same is true of any hitch (although the increase in receiver to trailer axle is only half of a PPP). I am not going to try and explain the math, as it gets very complicated very fast and is difficult to transfer by posts.
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Old 09-09-2020, 06:16 AM   #4
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My 27FB loaded for camping, full fresh water tank, ready to leave the driveway is always 1100 lbs tongue weight or more. That’s measured with a Sherline scale at the ball socket.
I use an Equal-I-Zer hitch, can’t comment on the Hensley, but it seems dznf0g has put some thought into it.
I’ve gone to the scale often enough to know my truck is still well within it’s capacity with that tongue weight, but I tow with an F-250. I’d be hesitant to pull that load with a passenger car.
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Old 09-09-2020, 09:32 AM   #5
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Hi

For a "shopping number" figure on 1,200 lb of tongue weight, including the hitch "stuff". You *might* get lucky and it'll come out a bit below that. If so you won the lottery. If it comes out at that number or a bit above, you don't need to buy a new tow vehicle. ....

The door sticker is the *only* way to get accurate numbers for a specific tow vehicle. The numbers you see on the internet are pretty much always over optimistic. Be very careful to read the fine print associated with those numbers. They include this and that buy maybe not something else.

For shopping purposes, Figure the trailer will be loaded to it's max rated weight. Be sure that the TV is rated to pull max trailer plus fully loaded vehicle. You *may* never hit these numbers, but a lot of us do indeed creep up on them.

Ideally, you would like to keep all the loads below 80% of the maximum ratings on the tow vehicle.. That's just a conservative engineer talking. Still, it *is* a really good idea if you can accomplish it.

Once you own all this stuff ( and it's obviously to late to change your mind ) a trip to the CAT scales is highly recommended. Regardless of all the math and stickers, what the scale tells you is the most trustworthy information.

Fun !!!

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Old 09-09-2020, 10:13 AM   #6
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Be careful when you shop for a tow vehicle. I’ve been down that road. I had done my research prior to shopping. The dealer will tell you anything to sell you a vehicle. For sure they’ll want to sell you one that they already have on their lot. Most sales people at dealers have no clue when you start talking about payloads, GBWR, GCWR, Curb Weights, etc. I ask a sales guy recently what’s the payload on they truck in the show room. He said “it’s a lot”. I said what’s a lot. He said 6,500 pounds. I said that’s 2000 pounds more that the truck weighs. He said “right. !!!!
I see why you’d like an SUV but my experience would tell you no. I look at SUVs as soccer mom and truck as work. Some manufacturers use the same frames for SUVs as for a line of cars. The brakes are undersized and won’t do it. Most SUVs have smaller engines, no integrated breaking systems, no towing packages with engine breaking, smaller gas tanks and you’ll most likely end up buying a generator for boondocking and you’ll have fuel cans and gas fumes inside your vehicle. Get a truck with a bed cover. I’d think Ford F-150 with total tow package, 3.5 eco boost with king cab. You won’t find one of those on a dealer lot. You’ll have to order one and wait about 2 months. With that said the total tow package you’ll get the 36 gallon gas tank. You’ll be thankful for the 36 gallon tank when you going across the west towing with gas stations few and far between. Good luck and welcome to The Forum.
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Old 09-09-2020, 10:42 AM   #7
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To the original question, the 791# hitch weight is for the 5868# stock TT (travel trailer), as built, with full propane and batteries; NO cargo, no water, and no hitch. So 5077#s is on the axles. This weight is determined by having the TT on a flat, level surface with scales under the tires and then having the trailer level and using a tongue weight scale under the ball coupler.

If you added a solar package, 2nd A/C, etc. then the base weight of the trailer will be more than the 5868# figure, and some of that additional weight will be on the hitch. (Obviously once you add cargo, water, etc. that additional weight will be distributed between the trailer axles and the hitch in some proportion depending on where the load is located.) All of this is without the TT connected to a TV (tow vehicle).

We have a ProPride 3P-1400 hitch, which is an improved version of the Hensley Arrow. It can handle up to 1400# of hitch weight. The 3P-1400 also weighs about 200#s and all of that weight is added to the hitch. We are below that limit, but around 1100# when loaded for travel, so glad we have that capacity to work with (2020 Flying Cloud 27' FBT). It also positions the trailer about 18" farther behind the TV receiver compared to a traditional ball hitch (I just measured it).
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Old 09-09-2020, 11:13 AM   #8
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tongue weight . . .

You can find SUVs that will do the job. Look at the Ford Expedition or Chevy Tahoe or Suburban with max trailering packages. I tow a 2011 28 Classic Rear Queen with a 2016 Tahoe 4WD with max trailer. With 1/2 tank of water, usual stuff in the trailer and bikes on the back plus 230 lbs of dog in the SUV, we are still within limits according to the CAT scales. I wouldn't do anything more without changing TV but we've been to all four borders with the rig - no problems. We cruise at 65 mph and do not try to race other rigs up and down the mountains . . . Do pay attention to the earlier suggestions about weight and only believe about 10% of what the sales people say unless you find someone who will sit down with you and who can do the math. i don't miss the larger gas tank since we stop anyway to refresh and stretch.
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Old 09-09-2020, 10:48 PM   #9
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Thanks very much everyone - most helpful
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Old 09-10-2020, 01:37 AM   #10
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Quote:
Originally Posted by NickA View Post
I'm currently excitedly waiting for a International 27FB to be delivered, and see that the spec quotes "Hitch Weight (w/ LP & Batteries)" as 791lbs. Does anyone know how this number is calculated? Is it with nothing in the trailer (based on the unloaded weight of 5868lbs), or assuming a relatively pessimistic distribution with the full GVWR of 7600lbs? I think it's the former


I'm planning to install a Hensley Arrow hitch (weighing ~190lbs). Does this mean that my car needs to have 791+190=981lb tongue weight capability? I need to purchase a towing vehicle and know trucks are the best options, but would prefer an SUV. However, looking at these numbers, I suspect this makes that impossible...

Thanks!
Nick
Tow ball weight should ideally be 10%-12% of your trailer's laden weight. It is associated with on-road stability.

Collyn
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Old 09-20-2020, 03:39 PM   #11
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TT Payload question

Need help with TV - TT Payload question. If I add trailer tongue weight to my TV Payload, do I also subtract this same tongue weight from my TT Payload? This seems logical but I have yet to read if this is proper or why this would not be the case.
Thank You All who contribute to this site! Iíve learned a lot...
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Old 09-20-2020, 04:34 PM   #12
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No you don't but the reason is due partially to convention and partially due to technical reasons. For the trailer the frame and structure and axles must support the trailer and payload so that is easy, follow the payload guidance. For the tow vehicle, payload while towing gets a little convoluted which is why many of us suggest using axle limits, towing limit, and gross combined limit for the tow vehicle. The payload number is more useful and straightforward when not towing.
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Old 09-22-2020, 03:20 AM   #13
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“For the tow vehicle, payload while towing gets a little convoluted which is why many of us suggest using axle limits, towing limit, and gross combined limit for the tow vehicle. The payload number is more useful and straightforward when not towing.”

That’s because you really don’t understand the physics of towing. If you did it would be clear.
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Old 09-22-2020, 07:55 AM   #14
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Thatís because you really donít understand the physics of towing. If you did it would be clear.
Really...You go play with the math and we will use published limits, compare with what our rig actually is and see if we are safe.
Much easier for the uninformed masses.

Bob
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Old 09-22-2020, 02:25 PM   #15
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Thank you BayouBiker for your timely advice. I’ve listed specifics for a 25 Ft Airstream and our present tow vehicle as related to weights - any and all comments please.

Weight Summary - as in Ready to tow:

TT has a Payload rating Greater than actual by 392 Lbs (32%)

TV GCVWR is Greater than actual by 463 Lbs (3.3%)

TV Rear Axle load rating is Greater than actual by 224 Lbs (5.3%)

TV Towing Capacity is Greater than actual by 92 Lbs (1.3%).
Not sure why but listed German tow capacity for this same G550 is rated at 4,000kg (8,800 Lbs) 1,800 Lbs greater than US spec trucks.

These first four weights are all marginally under Max limits however; TV Hitch Weight is spec’ed as 650#, and current 25Ft GT lists Tongue Weight at 882#, would this 36% over-weight item be a deal-breaker that would or should drive us to a 23Ft Globetrotter?

Your statement “follow TT payload guidance” is understood as
best practice. To that end; our favorite Airstream is their 25Ft Globetrotter with a calculated Payload (GVWR 7,300 less Base weight 6,074) of 1,226 Lbs. Prepping for a 7 day trip (in a rental Airstream) to a site with full hookups, (lacking a Cat scale) we weighed most and estimated a few items that would ride in the TT adding these to establish Payload weight. For this exercise I used tank holdings as containing (goal is to always empty before travel, we have yet to do the boon thing) - Fresh 10 Gal, Gray 5 Gal, Black 5 Gal. All this results with a TT Payload of 834 Lbs, which provides a 392 Lbs cushion as (32%) Under the spec’ed 25Ft Globetrotter Payload.

Our tow vehicle - a 2015 Mercedes G550 AWD, spec’s include:

Base Weight full fluids including gas 5,578 Lbs
GVWR 7,056
Calculated Payload (GVWR less Base) 1,478
Max Front axle load 3,150 (43% on Front)
Max Rear axle load 4,189 (57% on Rear)
Tires 265/60 R18 “E” rated at 3,000 Lbs each
Hitch Weight 650
Towing Capacity Max 7,000
GCVWR 14,056
G550 Wheelbase 112.2 inch

GCVWR rating = 14,056, is Greater than actual by 463# (3.3%)
(TV 5,578 + 1,108 actual PL + TT base 6,074 + 833 actual PL)

Tow capacity rating 7,000) is Greater than actual by 92#
(TT Base 6,074 + 834 TT Payload)

Axle limits; if TV ready to travel weighs 6,686 (Base 5,578 + Payload 1,108) and using standard 57% Rear distribution, Base Weight rear becomes 3,180# and if TV Payload is distributed 70% to Rear, this adds 776# of Payload to Rear Axle load, total Rear axle load becomes 3,965 Lbs. Max listed load of 4,189 Lbs is Greater than actual by 224# (5.3%).
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Old 09-22-2020, 04:02 PM   #16
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The MB G550 will pull that trailer safely and it will give you a great ride. The tongue limit is to discourage people from hitching a heavy travel trailer but we are going to move past that just a bit and make some other adjustments. Mercedes is trying to keep you from experiencing oversteer so we will have to do a few things to avoid it.

You're very close to the stability limits so you should take some reasonable measures to give yourself as much margin as you can get. Emergencies are very rare, especially if you give yourself some distance in front of you so you can react.

So here are some things you should do if you stick with the 25' plan.

Load your trailer to keep the tongue weight down. Shoot for under 12% tongue and get a good quality sway hitch. Propride is top of the line. You can also go with one that allows the ball to be very close to the bumper like the EAZ Lift Elite with sway control or the The Reese StraightLine and there are other excellent ones.

WD should be modest, not much tension.

Add 7 psi to the rear tires and run the front 2 psi under.

Bias the weight in the vehicle as forward as possible. Weight in the vehicle is good and will help with stability.

Run the trailer tires at about 52-55 psi. This will allow the trailer to slip just a bit on hard corners and track a little wide so it doesn't push the back of the vehicle so much.

As you get closer if you stick to this plan message me and we can cover a the rationale and I can give you more tips.
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Old 09-22-2020, 06:54 PM   #17
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Oh, my. I could not ask for a better assessment. I knew this combo was under yet close to limits, my read is we will be safe as long as the driver remains sane. Thank you so much.

May I ask, do you sell this knowledge or related products? The reason I ask; It’s simple, I’m like many others that want to do business with knowledgeable and friendly people and further when I need something I’m willing to pay...
Hardy Handshakes, 40Mike
PS - is it correct to assume the “Biker”part indicates a two wheeler parks close to an Airstream?
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Old 09-23-2020, 12:43 AM   #18
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Quote:
Originally Posted by BayouBiker View Post
The MB G550 will pull that trailer safely and it will give you a great ride. The tongue limit is to discourage people from hitching a heavy travel trailer but we are going to move past that just a bit and make some other adjustments. Mercedes is trying to keep you from experiencing oversteer so we will have to do a few things to avoid it.

You're very close to the stability limits so you should take some reasonable measures to give yourself as much margin as you can get. Emergencies are very rare, especially if you give yourself some distance in front of you so you can react.

So here are some things you should do if you stick with the 25' plan.

Load your trailer to keep the tongue weight down. Shoot for under 12% tongue and get a good quality sway hitch. Propride is top of the line. You can also go with one that allows the ball to be very close to the bumper like the EAZ Lift Elite with sway control or the The Reese StraightLine and there are other excellent ones.

WD should be modest, not much tension.

Add 7 psi to the rear tires and run the front 2 psi under.

Bias the weight in the vehicle as forward as possible. Weight in the vehicle is good and will help with stability.

Run the trailer tires at about 52-55 psi. This will allow the trailer to slip just a bit on hard corners and track a little wide so it doesn't push the back of the vehicle so much.

As you get closer if you stick to this plan message me and we can cover a the rationale and I can give you more tips.
Re: Add 7 psi to the rear tires and run the front 2 psi under. Now where have I read that before?

Ah yes - its in my posts and books!

Anyone else spotted the 'plagiarism' ?

Collyn
rvbooks.com
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Old 09-23-2020, 03:22 AM   #19
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Originally Posted by ROBERT CROSS View Post
Really...You go play with the math and we will use published limits, compare with what our rig actually is and see if we are safe.
Much easier for the uninformed masses.

Bob
🇺🇸
Robert, the full weight of the trailer tongue and the weight of the WDH count as payload on the TV. Is that too complicated for you? Thereís nothing convoluted about it and those that know the physics understand it.
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Old 09-23-2020, 04:28 AM   #20
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Calculating tongue weight requirements

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Originally Posted by Profxd View Post
Robert, the full weight of the trailer tongue and the weight of the WDH count as payload on the TV. Is that too complicated for you? Thereís nothing convoluted about it and those that know the physics understand it.


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